Musgrove was exemplary, retiring the first 10 batters he faced and allowing only one hit and no runs in 4 1/3 innings.
In addition, he tied a Major League record and set a club record with eight strikeouts as a reliever in his debut, surpassing Don Wilson's mark of seven, set in 1966.
"I loved the way he pitched," Astros manager A.J. Hinch said. "One heck of a debut that many around the game will watch tonight on TV and remark how impressive it was."
"He's nasty, man," McCullers said. "Plain and simple. Dude was filthy tonight."
Hinch said you couldn't have scripted a better debut for a pitcher from a performance standpoint, although he wasn't crazy about Musgrove having to warm up in front of a crowd of impatient fans.
"There's the tendency to go too fast and hurry through that because you have so many people in the stands, the umpires are waiting, the hitters are waiting. ... That's not a perfect time to come in and [say], 'Take a deep breath. You're about to make your Major League debut.' He didn't bat an eye."
Musgrove, who is listed at 6-foot-5 and 265 pounds, said his adrenaline was pumping, so much so that he already felt exhausted after jogging from the bullpen to the mound.
"I was tired," he joked.
After notching his first strikeout, fanning Blue Jays first baseman Edwin Encarnacion to end the inning, Musgrove tried to hide his excitement by placing his glove over his mouth. The TV cameras caught him screaming anyway.
"I was just trying to let out a loud scream," he said. "Just to let out whatever was inside, trying to calm down a little bit."
Jordan Ray is a reporter for MLB.com based in Houston. This story was not subject to the approval of Major League Baseball or its clubs.